The invention relates to multi-way valves for pumps for conveying heavy flowable materials of the kind having a shutter mechanism movable within a housing, the shutter mechanism having at one end at least one inlet which is movable across one or more housing openings and at the opposite end an outlet surrounded by a sealed contact joint which is movable across a delivery pipe opening in the housing, the contact joint surrounding the delivery pipe opening and contacting either the inside wall of the housing or a plate arranged on the inside wall of the housing in all intermediate and final positions of the control mechanism.
Multi-way valves of this kind control the flow of heavy flowable materials from a preliminary feed container to a drawing off delivery cylinder and from a compressing delivery cylinder to the delivery pipe. This invention relates more particularly, but not exclusively, to two-cylinder piston pumps in which the inlet and outlet of the shutter mechanism may be constituted by openings in two pipes which are coupled together and each define a respective conveying path, these pipes being jointly reciprocable either translationally or rotatably, in time with the piston stroke in the housing. Preferably, however, the invention is applicable to several embodiments of such multi-way valves, the shutter mechanisms of which at least partly combine the two conveying paths with each other and are either pivotable about an eccentric axis or movable translationally. The outlet, which has rounded off sides corresponding to the generally round interior opening of the delivery pipe, surrounds a surface which surrounds the delivery pipe in all phases of movement, so that the sealed contact joint does not overlap the edges of the delivery pipe opening.
Inside the shutter mechanism, the heavy flowable material undergoes excess pressure which, corresponding to the pressure in the delivery cylinders and the static pressure in the delivery pipe, is always greater than the pressure of the heavy flowable material surrounding the conveying device in the preliminary feed container, even when the column for conveying the heavy material is not in operation. The sealed contact joint must therefore be subjected to high pressure on its opposing sides in all phases of operation of the shutter mechanism in such a way that the overflowing of heavy material from the conveying device to the outside is avoided. This applies not only to the slurry contained in nearly all heavy flowable materials, but also to the particles which have an abrasive effect on the surfaces to be sealed. With regard to concrete, sand particles are the main concern. For this reason, the sealed contact joint is often not allowed to act directly on the inner face of the housing, but acts on a plate which is positioned on the housing wall. Nevertheless, it is claimed that, in spite of the abrasive particles in the heavy flowable material, a detrimental abrasion does not occur during sufficiently long operating times of the pump.
The invention proceeds from a previously known pump for heavy materials, which has a rotatable shutter as shutter mechanism which, as a result of the suitably adjusted varying distances of the inlet and outlet from the axis of the driving shaft, is related to a point on the shaft axis which is at least approximately free from momentum.
The outlet of the rotatable shutter has a kidney-shaped periphery which follows the sealing side of the sealed contact joint, so that this sealing side surrounds the delivery pipe opening but does not overlap its edges. With pumps for heavy flowable materials which, as a result of being extremely efficient, are suitable primarily for conveying concrete and mortar, the sealing of the outlet of the shutter mechanism has still presented a considerable problem.
The sealed contact joint is in the form of a hard seal, and cooperates with the hardened surface of the plate serving as protection against abrasion of the housing. However, it is still not possible to reduce the abrasive effect of the solid components of the heavy flowable material sufficiently for the desired working life of the apparatus to be obtained. The fine particles, that is in particular the sand particles in the case of concrete, penetrate between the surfaces which are to be sealed to each other and produce grooves in these surfaces which visibly increase during continuous operation of the pump, and which are responsible for very considerable abrasion of the sealed contact joint and wearing plate. This not only involves considerable expense in obtaining the necessary replacement parts, but also, in operation of such pumps, leads to leakages between the outlet of the rotatable shutter and the opening of the delivery pipe, which gives rise to breakdowns.
An object of the invention is therefore to reduce abrasion to a tolerable level by means of a multi-way valve of the kind described at the outset and to guarantee the sealing of the outlet of the rotatable shutter.